This invention relates generally to cooling and heating refrigeration systems and, more particularly, to a GAX absorption cycle with a secondary refrigerant.
Absorption cooling and heating systems are well known. In such a system operated in a cooling mode, a generator heats a refrigerant solution comprising a "strong" or concentrated solution of a more-volatile or refrigerant component in a less-volatile or solvent component. The heat drives the refrigerant from the strong solution to separate a refrigerant vapor, leaving a "weak solution" that is depleted of the refrigerant.
Where the refrigerant solution is a solution of a non-volatile solute in a volatile solvent, such as lithium bromide in water, the "weak solution" contains a higher concentration of the solute but a lower concentration of the solvent than the corresponding "strong solution." Where the refrigerant solution is a solution of a more volatile solute in a less-volatile solvent, such as ammonia in water, the "weak solution" is depleted of ammonia and is mostly water, while the "strong solution" is a more concentrated ammonia solution.
After being separated in the generator, the refrigerant vapor leaves the generator, flowing to a first phase change heat exchange device operated as a condenser. In the condenser the refrigerant vapor is placed under pressure and heat is removed to an external heat sink. As a result, the vapor condenses to form a refrigerant liquid. After leaving the condenser, the refrigerant liquid flows to a second phase change heat exchange device operated as an evaporator. The evaporator relieves the pressure on the refrigerant liquid and the refrigerant evaporates, again forming a vapor. This evaporation of the refrigerant draws heat from a heat load and creates the cooling effect of a refrigerator or air conditioner.
The refrigerant vapor from the evaporator flows to an absorber. The weak solution formed in the generator also flows to the absorber. In the absorber, the weak solution reabsorbs the refrigerant, reforming the strong solution. The strong solution then flows back to the generator and the cycle repeats.
The same system can be operated in a heating mode by reversing operation of the first and second phase change heat exchange devices such that the first phase change heat exchange device now operates as an evaporator and the second phase change heat exchange device operates as a condenser, with the associated heat inputs and outputs correspondingly also being reversed.
One refinement of such an absorption system is the incorporation of a device that functions as a generator to drive vapor from solution, as an absorber to absorb vapor into solution and as a heat exchanger to exchange heat between fluids. Such a device is sometimes referred to as a "GAX" device (e.g., generator-absorber-heat exchanger).
While the proper incorporation and use of a GAX device can improve cycle efficiency and performance, it has been desired to further increase the coefficient of performance (COP) of such a GAX cycle to thus make such a cycle more competitive with common vapor compression refrigerant technology as an attractive commercial heating and cooling technology.